[Qemu-devel] [PATCH v3 2/2] qapi: change QmpInputVisitor to QSLIST

[Paolo Bonzini <pbonzini@redhat.com>]

This saves a lot of memory compared to a statically-sized array,
or at least 24kb could be considered a lot on an Atari ST.
It also makes the code more similar to QmpOutputVisitor.

This removes the limit on the depth of a QObject that can be processed
into a QAPI tree.  This is not a problem because QObjects can be
considered truested; the text received on the QMP wire is untrusted
input, but the JSON parser already takes pains to limit the QObject tree
it creates.  We don't need the QMP input visitor to limit it again.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 qapi/qmp-input-visitor.c | 59 ++++++++++++++++++++++++------------------------
 1 file changed, 29 insertions(+), 30 deletions(-)

diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 21edb39..64dd392 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -30,6 +30,8 @@ typedef struct StackObject
 
     GHashTable *h;           /* If obj is dict: unvisited keys */
     const QListEntry *entry; /* If obj is list: unvisited tail */
+
+    QSLIST_ENTRY(StackObject) node;
 } StackObject;
 
 struct QmpInputVisitor
@@ -41,8 +43,7 @@ struct QmpInputVisitor
 
     /* Stack of objects being visited (all entries will be either
      * QDict or QList). */
-    StackObject stack[QIV_STACK_SIZE];
-    int nb_stack;
+    QSLIST_HEAD(, StackObject) stack;
 
     /* True to reject parse in visit_end_struct() if unvisited keys remain. */
     bool strict;
@@ -61,13 +62,13 @@ static QObject *qmp_input_get_object(QmpInputVisitor *qiv,
     QObject *qobj;
     QObject *ret;
 
-    if (!qiv->nb_stack) {
+    if (QSLIST_EMPTY(&qiv->stack)) {
         /* Starting at root, name is ignored. */
         return qiv->root;
     }
 
     /* We are in a container; find the next element. */
-    tos = &qiv->stack[qiv->nb_stack - 1];
+    tos = QSLIST_FIRST(&qiv->stack);
     qobj = tos->obj;
     assert(qobj);
 
@@ -100,18 +101,11 @@ static const QListEntry *qmp_input_push(QmpInputVisitor *qiv, QObject *obj,
                                         void *qapi, Error **errp)
 {
     GHashTable *h;
-    StackObject *tos = &qiv->stack[qiv->nb_stack];
+    StackObject *tos = g_new0(StackObject, 1);
 
     assert(obj);
-    if (qiv->nb_stack >= QIV_STACK_SIZE) {
-        error_setg(errp, "An internal buffer overran");
-        return NULL;
-    }
-
     tos->obj = obj;
     tos->qapi = qapi;
-    assert(!tos->h);
-    assert(!tos->entry);
 
     if (qiv->strict && qobject_type(obj) == QTYPE_QDICT) {
         h = g_hash_table_new(g_str_hash, g_str_equal);
@@ -121,7 +115,7 @@ static const QListEntry *qmp_input_push(QmpInputVisitor *qiv, QObject *obj,
         tos->entry = qlist_first(qobject_to_qlist(obj));
     }
 
-    qiv->nb_stack++;
+    QSLIST_INSERT_HEAD(&qiv->stack, tos, node);
     return tos->entry;
 }
 
@@ -129,10 +123,9 @@ static const QListEntry *qmp_input_push(QmpInputVisitor *qiv, QObject *obj,
 static void qmp_input_check_struct(Visitor *v, Error **errp)
 {
     QmpInputVisitor *qiv = to_qiv(v);
-    StackObject *tos = &qiv->stack[qiv->nb_stack - 1];
-
-    assert(qiv->nb_stack > 0);
+    StackObject *tos = QSLIST_FIRST(&qiv->stack);
 
+    assert(tos && !tos->entry);
     if (qiv->strict) {
         GHashTable *const top_ht = tos->h;
         if (top_ht) {
@@ -147,23 +140,23 @@ static void qmp_input_check_struct(Visitor *v, Error **errp)
     }
 }
 
-static void qmp_input_pop(Visitor *v, void **obj)
+static void qmp_input_stack_object_free(StackObject *tos)
 {
-    QmpInputVisitor *qiv = to_qiv(v);
-    StackObject *tos = &qiv->stack[qiv->nb_stack - 1];
+    if (tos->h) {
+        g_hash_table_unref(tos->h);
+    }
 
-    assert(qiv->nb_stack > 0);
-    assert(tos->qapi == obj);
+    g_free(tos);
+}
 
-    if (qiv->strict) {
-        GHashTable * const top_ht = qiv->stack[qiv->nb_stack - 1].h;
-        if (top_ht) {
-            g_hash_table_unref(top_ht);
-        }
-        tos->h = NULL;
-    }
+static void qmp_input_pop(Visitor *v, void **obj)
+{
+    QmpInputVisitor *qiv = to_qiv(v);
+    StackObject *tos = QSLIST_FIRST(&qiv->stack);
 
-    qiv->nb_stack--;
+    assert(tos && tos->qapi == obj);
+    QSLIST_REMOVE_HEAD(&qiv->stack, node);
+    qmp_input_stack_object_free(tos);
 }
 
 static void qmp_input_start_struct(Visitor *v, const char *name, void **obj,
@@ -224,7 +217,7 @@ static GenericList *qmp_input_next_list(Visitor *v, GenericList *tail,
                                         size_t size)
 {
     QmpInputVisitor *qiv = to_qiv(v);
-    StackObject *so = &qiv->stack[qiv->nb_stack - 1];
+    StackObject *so = QSLIST_FIRST(&qiv->stack);
 
     if (!so->entry) {
         return NULL;
@@ -376,6 +369,12 @@ static void qmp_input_optional(Visitor *v, const char *name, bool *present)
 static void qmp_input_free(Visitor *v)
 {
     QmpInputVisitor *qiv = to_qiv(v);
+    while (!QSLIST_EMPTY(&qiv->stack)) {
+        StackObject *tos = QSLIST_FIRST(&qiv->stack);
+
+        QSLIST_REMOVE_HEAD(&qiv->stack, node);
+        qmp_input_stack_object_free(tos);
+    }
 
     qobject_decref(qiv->root);
     g_free(qiv);
-- 
2.7.4